Looking for a way out of this mess

Full force ... hurricane Sandy moves northward through the Bahamas in this satellite image taken on October 26.

The reality of climate change is beginning to sink in. After two decades of theory-based predictions and computer modelling, a growing number of scientists now say we are seeing a profound shift in global weather patterns.

This northern summer, ice in the Arctic Ocean fell to a record low; for the first time, the entirety of the Greenland ice cap was in a state of thaw.

A recent paper has linked extreme weather events such as the droughts recently seen in North America and Russia - and some have argued the storms that have devastated America's east coast - to changes in climate. Professor Peter Wadhams, from Cambridge University, has referred to the predicted collapse of Arctic sea ice within four years as a ''global disaster''.

The question is: what do we do about it? For the quarter-century since global warming first impinged on the global consciousness, the answer has been to cut carbon emissions. Unfortunately, there is no sign of this happening. The rising population, combined with the increasing prosperity of the world's emerging economies, means it is unlikely we will be able to stabilise carbon dioxide levels before they have broken the 500 parts per million barrier (they now stand at fewer than 400 parts per million). The likelihood is that over the next 200 years, we will see global temperatures rise between 2 degrees and 6 degrees, the latter figure representing a catastrophe for civilisation.

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As a result, an idea that has been on hold for some time is coming to the fore. If we cannot - or more accurately will not - cut greenhouse gas emissions, might it be possible to ameliorate the effects of rising CO2 directly, by ''geoengineering'' the Earth?

So far, the idea of grabbing CO2 out of the atmosphere, shielding the planet with mirrors or seeding the oceans with carbon-eating iron, has seemed like science fiction - and dangerous science fiction at that. Many scientists and campaigners are suspicious of a technological ''fix'' for climate change, on the grounds it could make things even worse, or at least encourage complacency.

But with dangerous climate change looming, these outlandish ideas are now being taken far more seriously. Proposals on the drawing board include whitening clouds with sea spray to reduce the amount of sunlight hitting the surface, reflecting sunshine with space-based mirrors, and seeding the ocean with minerals that will absorb more CO2.

Some of these ideas amount to no more than impressive-looking diagrams in science magazines. Placing millions of space mirrors in orbit, for instance, would be completely impractical, ludicrously expensive and risk catastrophic environmental damage from the thousands of rocket launches required.

But other projects are surprisingly feasible. For example, injecting particles of salt into clouds would, in theory, encourage more water droplets to form around them, thickening and whitening the clouds and reflecting more sunlight into space. Or we could get the sea to dispose of our carbon. In 2004, scientists seeded 168 square kilometres of the Southern Ocean with iron sulphate in what was called the European iron fertilisation experiment. The iron encouraged the growth of phytoplankton, which removed CO2 from the atmosphere through photosynthesis. When the algae died, they sank to the sea floor, locking the carbon away.

In the middle of this year, Oxford University, which set up a geoengineering program in 2010, presented some of the more realistic proposals. Oxford has been involved in several government-funded geoengineering projects. One, known as Spice - Stratospheric Particle Injection for Climate Engineering - is based on the fact that volcanic eruptions can cool the planet (a sign there may be a relatively simple ''cure'' for global warming). When Mount Pinatubo in the Philippines erupted in 1991, it released 20 million tonnes of sunlight-blocking sulphur dioxide; global temperatures temporarily dropped 0.5 degrees.

Spice was intended to use climate simulations and tethered balloons to artificially create a similar effect. The first test was planned for October last year. This would have involved injecting water droplets into the atmosphere about 1000 metres up, via a pipe, to test the technology. Despite the fact that this would have had no environmental impact, it attracted the wrath of several green groups, who saw it as the thin edge of a climate-tampering wedge. The team delayed the test and then cancelled it in May. ''A lot of people were circling around it,'' the project leader Dr Matt Watson, of the University of Bristol, says.

It is not just environmental activists. Many scientists also have profound concerns about the safety of geoengineering. Tim Palmer, of Oxford University, told New Scientist recently that, according to climate change models, any form of sunshade has the potential to bring famine to billions - or ''turn the Amazon to desert''.

When proposals to alter the planet deliberately - in effect, to terraform Earth back to its pre-industrial state - were first aired, there was a horrified reaction from many researchers.

In 2008, Professor Alan Robock, from Rutgers University in New Jersey, wrote a paper in the Bulletin of the Atomic Scientists entitled ''Twenty reasons why geoengineering may be a bad idea''. The potential dangers, he pointed out, included marine acidification, ozone depletion, human error and military use of ''weather control'' technology.

''I don't think geoengineering is a solution,'' Robock now says. ''If solar radiation management could be implemented - it is an imaginary, unproven technology - it could produce benefits and risks, and we do not know whether the benefits would outweigh the risks.''

Yet not all suggested geoengineering solutions are complex. Some involve simply covering roofs and roads with solar-reflective paint, an idea championed by Steven Chu, Barack Obama's Energy Secretary (and a Nobel-winning physicist). There are doubters, but it does have the advantage of being a simple, cheap - and safe - fix.

Then there are also those who put their faith in carbon capture and storage (CCS). This involves either removing the gas from the atmosphere directly, or stripping it out of the exhaust chimneys of fossil-fuel-burning power stations.

While it is the latter on which Britain is pinning its hopes of building a new generation of gas-fired power stations without breaching emissions targets, the former is also technically feasible, if expensive. Richard Branson's Virgin Earth Challenge offered $25 million for a commercially viable design to scrub CO2 from the air, announcing its shortlist in June after more than 10,000 submissions. The British government is about to reveal the results of its own competition, although this one focused on how to stop CO2 from power plants getting into the atmosphere in the first place.

Professor Jon Gibbins, from the University of Edinburgh, says ''air capture'' is the only way of actually reducing the amount of CO2 in the atmosphere. ''But,'' he adds, ''it's expensive. It's not a get-out-of-jail-free card. The problem is that people are not prepared to spend as much money on getting low-carbon electricity via CCS as they are via renewables. If they were, we would have had carbon capture and storage widely deployed by now.''

In Canada, efforts are more advanced. SaskPower is building the world's first CCS coal plant and the oil giants Shell, Chevron and Marathon have started building Quest, a CCS project near Shell's Athabasca oil sands operations. Its aim is to capture a million tons of CO2 annually and transfer it by pipes to underground storage wells.

Outright scepticism about the reality of climate change is on the wane; while scientists still argue about the likely effects, and degree, of global warming, no serious researchers now say that we can carry on as we are.

But a new front has opened in the climate wars - between those who say the only way out of this mess is to change our ways, and those who say this is unrealistic, and that just as technology got us into this mess, only technology can get us out of it.

If we do decide to go down the geoengineering route, we had better hope the cure is not worse than the disease.